The present invention refers to a mechanism for eliminating impurities from fibrous material, in particular cotton, having at least two card-clothed rolls arranged after a feed mechanism, and a screening drum to which the fibrous material is fed by means of an airstream, where the two card-clothed rolls are closely enclosed by a housing interrupted by separating openings having associated separating edges. The second card-clothed roll cooperates with the first card-clothed roll as a take-off and loosener roll for the fibrous material and the centrifugal forces at the circumference of the second card-clothed roll are greater than at the first card-clothed roll. Associated with the two card-clothed rolls is a third card-clothed roll which is closely enclosed by a housing interrupted by separating openings and is associated in such a way that between the first and the third card-clothed rolls a carding action is exerted upon the fibrous material, in accordance with the Parent Patent (German Patent Application No. P 27 12 650.726).
With this mechanism it is possible in a single cleaning mechanism and with only one passage of the fibrous material, to free the latter of all impurities, in that in individual stages of elimination first of all the coarse, then finer and finally fine and finest impurities get removed from the fibrous material which is loosened down to individual fibers. By the foreseen arrangement of the third card-clothed roll in the way that the fibrous material gets carded between it and the first card-clothed roll and the take-off and loosener roll cooperating with the two carding card-clothed rolls, the flow of material is increased and a still more thorough elimination of coarser impurities is achieved.
But it has been found that in doing this in certain cases neps may form in the fibrous material, the loosening of which on the succeeding machines is only partially possible and which therefore, impair the quality of the yarn produced.